The invention relates to a process for monitoring the function of a sensor module, which is constructed as a solid state integrated circuit and which has a sensor and at least one measuring amplifier, wherein the sensor module has external connections at least for the power supply and for an output measurement signal.
The sensor module used for this can, in particular, involve a module having a magnetic field-dependant sensor, but sensor modules with other sensors, for example an optical sensor, a pressure sensor or the like, can also be used.
Sensor modules with magnetic field sensors (for example with a Hall sensor) are used, among other things, in the motor vehicle sector in camshaft/crankshaft applications or in ABS-systems. The rotational movement in these leads, for example, through a combination of rotating toothed gear and stationary magnets at the site of the sensor, to a magnetic signal that consists of a DC portion and an AC portion. By measurement of the AC portion, which is accomplished with static differential sensors having two magnetically sensitive surfaces or dynamic sensors having one magnetically sensitive surface, the rotational movement is converted, for example by the Hall effect, into a voltage that leads, in a sensor module with a digital output measurement signal, through a Schmitt trigger circuit, to a switching operation at the output of the sensor module.
As a function of the ambient temperature of the sensor module, which can be installed in the engine compartment of a motor vehicle, for example, the separation distances of the toothed gear-magnet sensor-magnet can change, so that both the AC portion and the DC portion of the magnetic field are changed at the site of the magnet sensor. This can also occur through wear of a mechanical component in the course of the operating time. This drop in the AC portion caused by outside circumstances can lead to a sudden breakdown in the function of the application, when, for example, in a sensor module having a digital output, the value falls below a certain threshold value.
Such a breakdown of the system can, for example in motor management, result in considerable operational damages and also safety problems. The function of the sensor itself, in its parameters, is not the cause for a breakdown in these cases, but instead the ambient conditions changing in the surroundings of the sensor. The possibility for function monitoring is thus limited to the monitoring of the output measurement signal and thus to its presence in a sensor input signal.
An object of the present invention is to create a process for monitoring the function of a sensor module, as well as a sensor module suitable for this, so that an expanded monitoring of the function is possible, which also allows recognition of changing ambient conditions, so that countermeasures can be taken at the proper time prior to function breakdown. In the process, the expense for the sensor module should remain practically unchanged, and also its respectively provided structural shape should be kept.
In order to achieve these objectives, it is proposed in view of the process that circuit measurement values available within the sensor module be superimposed as modulation signals on the supply current and/or the supply voltage and/or the output measurement signal, and be output via the available external connections as diagnostic signals, and that either the internal circuit measurement values be output as analog or digital modulations and the output measurement signal be output as a digital value, or that the internal circuit measurement values be output as digital modulations and the output measurement signal be output as an analog value.
Using the internal circuit measurement values, the tendency of the measurement conditions of the sensor module to change can be recognized at the proper time in advance, here prior to a breakdown of sensor function, i.e. before the output measurement signal can no longer be evaluated or is no longer present. The internal circuit measurement values, which allow recognition of the changing ambient conditions, are superimposed on the output measurement signal as modulation, for example. Thus, a corresponding diagnostic signal is available to the outside. By the modulation of the output signal, optionally also of the supply current or the supply voltage, the functional values remain unchanged, so that there is no interruption of the measuring function or the output measurement signal. It is further advantageous that the available connections for the output of the diagnostic signal be used as well, and consequently, that the structural shape of the sensor module and its connection configuration remain unchanged.
Expediently, for a digital output measurement signal, at least one measurement value proportional to the sensor signals is collected as a circuit measurement value and is output as a diagnostic value via the available external connections. The digital output measurement signal is only available when the amplitude of the sensor signal exceeds a respective preset threshold value. If this threshold value is not reached, then accordingly no more output signals are emitted and a sudden function breakdown is the result. Since, however, according to the invention, a measurement value proportional to the sensor signal is collected inside the circuit as a circuit measurement value and is available externally as a diagnostic signal, the danger can be recognized, in the present case, at the proper time prior to function breakdown using a changing amplitude of the sensor signal, and corresponding countermeasures can be taken.
There is also the possibility, however if necessary, that in combination with the aforementioned measure, an offset voltage or the offset current, the temperature, filter coefficients and similar internal operating data of the circuit are collected as circuit measurement values and output as a diagnostic signal via the available external connections. Also in these internal circuit measurement values, changing external ambient conditions can be recognized.
A further refinement of the process according to the invention provides that the diagnostic signal be called up from the outside via the available external connections, in particular by means of a call-up (request) modulation signal that can be supplied via the available outside connections. In many applications, changes of ambient conditions are only expected at longer time intervals, so that it is sufficient herein to call up diagnostic values at predetermined time intervals.
The invention also relates to a sensor module which is constructed as a solid state integrated circuit and has a sensor as well as at least one measuring amplifier, wherein the sensor module has external connections at least for power supply and for the output measurement signal.
This sensor module is characterized according to the invention in that in the sensor module an evaluation circuit is provided, which is connected to at least one internal measurement point of the circuit, and that the evaluation circuit is connected to a modulator for the modulation of the supply current and/or the supply voltage and/or the output measurement signal, in order to output a diagnostic signal, which is formed from an internal circuit measurement value, via the available external connections of the sensor module.
As already explained in connection with the process according to the invention, in this sensor module according to the invention, via the available external connections, aside from the output measurement signal, an access to internal circuit measurement points is also available, and the measurement values available through it make possible a diagnosis of circuit function. In particular, it is thereby recognizable at what (safety) distance the circuit is operating from its operating limits. From that the appropriate countermeasures can be taken at the proper time prior to breakdown of the operating function. By modulating up the diagnostic values to the available measurement quantities or supply quantities, no additional connections are necessary, so that the structural shape of the sensor module and its connection configuration can remain unchanged. In the given applications, the sensor modules used until now can thus be replaced without problems by the sensor modules according to the invention, without changes to the circuit being necessary.
An advantageous use of a sensor module according to the invention is available for a rotational speed measurement with simultaneous distance measurement of the sensor or the sensor module from an emitter. For example, such a use is possible in a motor vehicle, that is equipped with an ABS-system, wherein the rotational speed of the rims is measured using magnetic field sensors. The rotation is measured with a toothed gear that has the same rotational speed as the wheel itself. The wear and tear on the brake lining causes larger activation paths to result for the brake cylinder over the course of the useful life of the brake lining. By the coupling of this movement with the position of the sensor provided for the rotational speed measurement, the possibility is created to detect, using a single sensor, both the rotational movement and the change in the amplitude (AC portion), which becomes adjusted by the distance change for brake linings that wear over time.